Commit d5e97a1d2c79 ("Build: define IMAGE_AT_EL1 or IMAGE_AT_EL3
globally for C files") does not have commit 848a7e8ce1d9 ("Build:
introduce per-BL CPPFLAGS and ASFLAGS") as an ancestor because
they were pulled almost at the same time.

This is a follow-up conversion to be consistent with commit
11a3c5ee7325 ("plat: pass -D option to BL*_CPPFLAGS instead of
BL*_CFLAGS").

With this change, the command line option, IMAGE_AT_EL3, will be
passed to .S files as well.

I remove the definition in include/lib/cpus/aarch64/cpu_macros.S

Otherwise, the following error would happen.

  include/lib/cpus/aarch64/cpu_macros.S:29:0: error: "IMAGE_AT_EL3" redefined [-Werror]

Change-Id: I943c8f22356483c2ae3c57b515c69243a8fa6889
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>